Product Code Database
An electrical cable is an assembly of one or more running side by side or bundled, which is used as an electrical conductor to carry electric current.
Electrical cables are used to connect two or more devices, enabling the transfer of Signal, Electric power, or both from one device to the other. Physically, an electrical cable is an assembly consisting of one or more conductors with their own insulations and optional screens, individual coverings, assembly protection and protective covering.
One or more electrical cables and their corresponding connectors may be formed into a cable assembly, which is not necessarily suitable for connecting two devices but can be a partial product (e.g. to be soldered onto a printed circuit board with a connector mounted to the housing). Cable assemblies can also take the form of a cable lacing or cable harness, used to connect many terminals together.
Physically, an electrical cable is an assembly consisting of one or more conductors with their own insulations and optional screens, individual coverings, assembly protection and protective coverings. Electrical cables may be made more flexible by stranding the wires. In this process, smaller individual wires are twisted or braided together to produce larger wires that are more flexible than solid wires of similar size. Bunching small wires before concentric stranding adds the most flexibility. Copper conductor may be bare, or they may be plated with a thin layer of another metal, most often tin, but sometimes gold, silver or another material. Tin, gold, and silver are much less prone to Redox than copper, which may lengthen wire life, and makes easier. Tinning is also used to provide lubrication between strands. Tinning was used to help removal of rubber insulation. Tight lays during stranding makes the cable extensible (CBA – as in telephone handset cords).
In the 19th century and early 20th century, electrical cable was often insulated using cloth, Natural rubber or paper. Plastic materials are generally used today, except for high-reliability power cables. The first thermoplastic used was gutta-percha (a natural latex) which was found useful for underwater cables in the 19th century. The first, and still very common, man-made plastic used for cable insulation was polyethylene. This was invented in 1930, but not available outside military use until after World War 2 during which a telegraph cable using it was laid across the English Channel to support troops following D-Day.Ash, Stewart, "The development of submarine cables", ch. 1 in, Burnett, Douglas R.; Beckman, Robert; Davenport, Tara M., Submarine Cables: The Handbook of Law and Policy, Martinus Nijhoff Publishers, 2014 .
Cables can be securely fastened and organized, such as by using trunking, , or cable lacing. Continuous-flex or used in moving applications within can be secured using Cable management or cable ties.
The first solution to these problems is to keep cable lengths in buildings short since pick up and transmission are essentially proportional to the length of the cable. The second solution is to route cables away from trouble. Beyond this, there are particular cable designs that minimize electromagnetic pickup and transmission. Three of the principal design techniques are shielding, Coaxial cable geometry, and Twisted pair geometry.
Shielding makes use of the electrical principle of the Faraday cage. The cable is encased for its entire length in foil or wire mesh. All wires running inside this shielding layer will be to a large extent decoupled from external electrical fields, particularly if the shield is connected to a point of constant voltage, such as earth or ground. Simple shielding of this type is not greatly effective against low-frequency magnetic fields, however - such as magnetic "hum" from a nearby power transformer. A grounded shield on cables operating at 2.5 kV or more gathers leakage current and capacitive current, protecting people from electric shock and equalizing stress on the cable insulation.
Coaxial design helps to further reduce low-frequency magnetic transmission and pickup. In this design the foil or mesh shield has a circular cross section and the inner conductor is exactly at its center. This causes the voltages induced by a magnetic field between the shield and the core conductor to consist of two nearly equal magnitudes which cancel each other.
A twisted pair has two wires of a cable twisted around each other. This can be demonstrated by putting one end of a pair of wires in a hand drill and turning while maintaining moderate tension on the line. Where the interfering signal has a wavelength that is long compared to the pitch of the twisted pair, alternate lengths of wires develop opposing voltages, tending to cancel the effect of the interference.
CENELEC HD 361 is a ratified standard published by CENELEC, which relates to wire and cable marking type, whose goal is to harmonize cables. Deutsches Institut für Normung (DIN, VDE) has released a similar standard (DIN VDE 0292).
|
|
